Curing of adhesives based on conjugated diolefins and, optionally including vinyl aromatics has increased the range of service properties for these adhesives. Radiation curing and chemical curing are known. This curing causes covalent crosslinking of the polymerized conjugated diolefins which is evidenced by a high gel content of the crosslinked polymer. Before crosslinking, the polymers are melt processable but after crosslinking, the gels can not be processed as melts. Crosslinking therefore enhances solvent resistance and improves elevated temperature shear properties. The compositions can therefore be applied to a substrate in a melt and then crosslinked to form a superior adhesive. However, improvements in the adhesives could be made if the adhesives could be cured at lower dosages of radiation or lower levels of chemical curing agents.
Further, the known curable adhesives which are based on conjugated diolefin block copolymers do not have particularly good long term heat, weather and ultraviolet stability due to the need to utilize unhydrogenated polymers having one residual aliphatic double bond per polymerized unit. The known vinyl aromatic-conjugated diolefin block copolymer based adhesives which are curable are unhydrogenated polymers. Hydrogenation is known to improve long term heat, weather and ultraviolet stability, but it removes the double bonds which are needed to effect the curing. Such curing methods are not effective when the polymers are hydrogenated. The requirement for this unsaturation is particularly evident when typical tackifiers are present in the composition because their presence generally inhibits radiation crosslinking of the hydrogenated polymer.
It is therefore an object of the present invention to provide a crosslinked polymeric composition which is melt processable before crosslinking and has a high gel content after crosslinking. In another aspect, it is an object to provide a process to prepare this crosslinked polymeric composition. In another aspect, it is an object of this invention to provide an adhesive composition which is melt processable before crosslinking and which has a high gel content after crosslinking.